Fiber-reinforced plastics (FRPs) are materials in which a matrix resin, such as a thermosetting resin or a thermoplastic resin, and a reinforcing fiber are integrated, and which are used in various fields for their light weight and superiority in terms of strength properties. Examples of the thermosetting resin that may be used include unsaturated polyester resins, epoxy resins, polyimide resins, and the like. Examples of the thermoplastic resin include polyethylene, polypropylene, polyamide, and the like. Examples of the reinforcing fiber may include carbon fibers, glass fibers, aramid fibers, and the like.
Hollow parts have been fabricated using fiber-reinforced plastics, and one of the molding methods thereof is internal pressure molding. Internal pressure molding is a method in which a hollow molding material is placed inside a cavity of a mold, internal pressure is applied from the inside of the hollow material to place the hollow material in close contact with the mold, and heat molding is performed under those conditions.
Patent Document 1 discloses an example in which a fiber-reinforced plastic hollow part with a varying cross-section is molded using internal pressure molding. In Patent Document 1, a prepreg is wound around a mandrel with a circular cross-section, and the mandrel is thereafter pulled out to produce a prepreg hollow part. A pressurizing bag is inserted into a hollow portion of the prepreg hollow part. The hollow part into which the pressurizing bag is inserted is placed inside a metal mold having a shape that accommodates the varying form of the hollow part, the metal mold having a filler prepreg disposed at the varied-form portion. By subsequently performing molding through internal pressure molding, an FRP hollow part with homogeneous cross-section variation is obtained.
Patent Document 2 discloses a structural member used in building constructions and a manufacturing method therefor. In Patent Document 2, there is produced a fabric in which a reinforcing fiber is, by braiding, wound around a hollow cylindrical liner (mold material) made of a stretchable material such as a thermoplastic resin or the like. After the fabric is placed inside a mold, a resin is impregnated into the reinforcing fiber and cured. During resin impregnation, pressurized air is supplied into the liner (mold material) to prevent the liner from being deformed.
Patent Document 1: JP Patent Publication (Kokai) No. 2006-123475 A
Patent Document 2: JP Patent Publication (Kokai) No. 2003-328498 A